Method For Purifying Nitrogen Trifluoride

Abstract

A highly pure nitrogen trifluoride having a carbon tetrafluoride content of 10 ppm or less can be effectively obtained by boiling crude liquid nitrogen trifluoride having carbon tetrafluoride contaminant under a pressure ranging from 35 to 45 atm, to remove carbon tetrafluoride therefrom through vaporization.

Description

TECHNICAL FIELD[0001]The present invention relates to an efficient method for purifying nitrogen trifluoride contaminated by trace carbon tetrafluoride.BACKGROUND ART[0002]Nitrogen trifluoride (NF3), which is widely used in the step of cleaning a CVD (chemical vapor deposition) device or etching a semiconductor in electronic component industry, is generally prepared by reacting fluorine (F2) with ammonia (NH3) or / and an ammonium salt, or by direct electrolysis of ammonium fluoride. Nitrogen trifluoride thus obtained contains about 10-100 ppm of carbon tetrafluoride (CF4) impurity.[0003]The recent demand of ultra-high purity nitrogen trifluoride requires that the concentration of carbon tetrafluoride be 10 ppm or less.[0004]However, as the boiling points of nitrogen trifluoride and carbon tetrafluoride are very similar, −129° C. and −128° C., respectively, differing by a mere 1° C., and the molecular sizes and polarities thereof are also similar, it has been very difficult to remove ...

AI Technical Summary

Benefits of technology

[0007]In accordance with the method of the present invention, ultra-high purity nitrogen trifluoride having a carbon tetrafluoride content of 10 ppm or less can be effectively and economically obtained.

Problems solved by technology

However, as the boiling points of nitrogen trifluoride and carbon tetrafluoride are very similar, −129° C. and −128° C., respectively, differing by a mere 1° C., and the molecular sizes and polarities thereof are also similar, it has been very difficult to remove carbon tetrafluoride from nitrogen trifluoride by a conventional industrial distillation or absorption process.